Welding Consumables-Welding-Lecture Handouts-Lectrue Handout , Exercises for Welding Technologies
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Welding Consumables-Welding-Lecture Handouts-Lectrue Handout , Exercises for Welding Technologies

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This lecture handout was provided by Harijatha Mehta at Bengal Engineering and Science University for Welding course. It includes: Welding, Consumables, Coated, Electrodes, Filler, Rods, Flux, Shielding, Gases, Compositi...
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7-1

7. WELDING CONSUMABLES

7.1 WELDING CONSUMABLES

Welding consumables are materials used up during welding such as electrodes, filler rods, fluxes and externally applied shielding gases.

In almost all the developed countries, national codes and standards have been developed to clearly identify the specifications for various uses. However, in the preceding paragraphs, division will cover, the most common codes amongst all, i.e. the specification outlined by the American Welding Society.

The first specification for mild steel covered electrodes “A4.1 specifications for carbon steel electrodes for shielded metal arc welding” by American Welding Society. As the welding industry expanded and number of types of electrodes for welding steel increased, it became necessary to devise a system of electrode classification to avoid confusions.

The process like gas tungsten arc welding consume the electrodes at considerably low rate, hence it is not common to include such electrodes as consumables. However, the filler wire, if used, with these, so called, non-consumable electrodes is obviously a consumable item. The welding consumables can be grouped under will include four major categories, i.e.

i) Coated electrodes

ii) Fluxes

iii) Filler wires/filler rods

iv) Shielding gases

See Table 7.1 for AWS Filler Metal Specifications.

7.2 FACTORS TO BE CONSIDERED FOR SELECTION OF ELECTRODES

7.2.1 Base Metal Strength Properties

Know and match mechanical properties

It is essential to know not only the kind of metal being welded (e.g. mild steel or cast iron etc) but also its mechanical properties.

Mild steel ----------- generally E60XX or E70XX electrodes match base metal.

Low alloy steel ----- select electrodes that match base metal properties.

7.2.2 Base Metal Composition

Know and match composition

Mild Steel- Any E60XX or E70XX electrode is satisfactory. Low alloy steel - select electrode that most closely match base metal composition.

7.2.3 Welding Position

Match electrode to welding position encountered

Not all electrodes are designed for use in every position. Electrode must match the welding position being used.

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7.2.4 Welding Current

Match power supply available

The electrode selected should be one that closely matches the type of power source being used. The type of welding current to be used with the particular electrode is indicated by AWS electrode classification.

Some electrodes are designed for D.C. others A.C, ; some either. Observe correct polarity.

Table 7.1: AWS filler metal specifications.

AWS DESIGNATI ON

TITLE OF SPECIFICATION AWS

DESIGNAT ION

TITLE OF SPECIFICATION

A5.01 Filler Metal Procurement Guidelines A5.16 Specification for Titanium and Titanium Alloy Welding Electrodes and Rods

A5.1 Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding

A5.17 Specification for Carbon Steel Electrodes and Fluxes for Submerged Arc Welding

A5.2 Specification for Carbon and Low Alloy Steel Rods for Oxyfuel Gas Welding

A5.18 Specification for Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding

A5.3 Specification for Aluminum and Aluminum Alloy Electrodes for Shielded Metal Arc Welding

A.519 Specification for Magnesium Alloy Welding Electrodes and Rods

A5.4 Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding

A5.20 Specification for Carbon Steel Electrodes for Flux Cored Arc Welding

A5.5 Specification for Low Alloy Steel Electrodes for Shielded Metal Arc Welding.

A5.21 Specification for Bare Electrodes and Rods for Surfacing

A5.6 Specification for Copper and Copper Alloy Electrodes for Shielded Metal Arc Welding

A5.22 Specification for Stainless Steel Electrodes for Flux Cored Arc Welding

A5.7 Specification for Bare Copper and Copper Alloy Electrodes and Rods

A5.23 Specification for Low Alloy Steel Electrodes and Fluxes for Submerged Arc Welding

A5.8 Specification for Brazing Filler Metals A5.24 Specification for Zirconium and Zirconium Alloy Welding Electrodes and Rods

A5.9 Specification for Bare Stainless Steel Welding Electrodes and Rods

A5.25 Specification for Carbon and Low Alloy Steel Electrodes and Fluxes for Electroslag Welding

A5.10 Specification for Bare Aluminum and Aluminum Alloy Welding Electrodes and Rods

A5.26 Specification for Carbon and Low Alloy Steel Electrodes for Electrogas Welding

A5.11 Specification for Nickel and Nickel Alloy Electrodes for Shielded Metal Arc Welding

A5.27 Specification for Copper and Copper Alloy Rods for Oxyfuel Gas Welding.

A5.12 Specification for Tungsten Electrodes for Arc Welding and Cutting

A5.28 Specification for Low Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding

A5.13 Specification for Surfacing Electrodes for Shielded Metal Arc Welding.

A5.29 Specification for Low Alloy Steel Electrodes for Flux Cored Arc Welding.

A5.14 Specification for Bare Nickel and Nickel Alloy Welding Electrodes and Rods

A5.30 Specification for Consumable Inserts.

A5.15 Specification for Welding Rods and Shielded Metal Arc Electrodes for Cast Iron

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7.2.5 Joint Design and Fit-Up

Select for penetration characteristic - digging, medium or light.

The design of joint and fitup determines the degree of arc penetration.

No beveling or tight fit up - use digging. Thin materials or wide root opening - light soft arc. Electrode that gives the required penetration should be selected.

The number of passes is also determined by the type of electrode selected. Multiple passes require more current than a single pass.

7.2.6 Thickness and Shape of Base Metal

To avoid weld cracking on thick and heavy material of complicated design, select electrode with max. ductility. Low hydrogen process of electrodes are recommended. The thicker the metal, the greater the current i.e. required to produce a suitable weld. An increase in the amount of current requires a corresponding increase in electrode diameter size.

7.2.7 Service Condition and Specifications

Determine service conditions - low temp., High temp. Shock loading - match base metal composition, ductility and impact resistance. Use low hydrogen process also, check welding procedure or specification of electrode type.

7.2.8 Production Efficiency and Job Conditions

For high deposition and most efficient production under flat position requirements, select a high iron powder type of large diameter wires. For other conditions, you may need to experiment with various electrodes and sizes.

7.3 ELECTRODES STANDARDS

In the world industry countries make their national welding standards e.g.

AWS is the standard which is prepared by American Welding Society.

DIN is the German Industry Standard.

JIS is the Japan Industry Standard.

7.4 SMAW ELECTRODES

About half of all filler metals used as stick electrodes. Stick - electrode welding is the single most frequently used welding process.

The amount of stick electrodes welding done drops a little each year relative to other processes, as the cost of welding labor goes up and manufacturer move to one or more of the semi automatic or automatic processes to increase productivity. Nevertheless, SMAW still holds a large share of total welding filler metal business. Here we shall give more concentration on the SMAW electrodes.

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7.4.1 Anatomy of a SMAW Electrode

An electrode for welding steel or cast iron will have a mild-steel core wire. An aluminum electrode would have an aluminum core wire. An SMAW electrode for welding copper or copper alloys will have a copper core wire.

Similarly, an electrode for welding any other metal probably would have a relatively pure (as opposed to an alloy) core wire made out of that metal. There are several reasons why?

A high alloy core wire would be very expensive to make. Many alloys can’t even be made into wire; they are not ductile enough. In addition, there’s no need to buy small quantities of many different kinds of alloy-steel, alloy-aluminum, or bronze wires when the SMAW flux coating can be used to add the alloying elements.

When the welding arc forms between the electrode and the base metal, part of the flux on the hot working end of the electrode is vaporized, making a protective shielding gas that surrounds the hot weld metal, the heat-affected zone of the base metal next to the weld, and the molten end of the electrode wire. Other elements in the flux join with the molten core wire to make weld metal with the desired final properties.

For example, an austenitic stainless steel electrode will use a mild-steel core wire, but the chromium and other elements like nickel that make stainless steel, austenitic, will be added to the weld metal from the flux.

7.5 FLUXES

7.5.1 Definition of Flux

According to British standard 499, the definition of flux is a material used during welding, brazing or braze welding to clean the surfaces, the joint chemically, to prevent atmospheric oxidation and reduce impurities or float them to the surface. In arc welding, many other substances which perform special functions are added to the flux mixture.

7.5.2 Fluxes are Used in Four Main Welding Process

a) Manual metal - arc-welding electrode; the flux is coated to the outside of a filler metal rod. b) Submerged arc welding fluxes: added separately in the weld pool.

c) Flux cored are welding; the flux is wrapped inside a continuous wire sheath.

d) Electro-slag welding: the fairly large granules of flux are again entirely separate from the wire.

All these processes require different physical and chemical properties, from the flux; however many minerals used in flux formulations are common to all four flux processes and have the same or a similar role to play in all of them.

7.5.3 The Constituents of Flux

The majority of welding fluxes for steel are made from minerals, with as little purification and treatment as possible; this keep down the cost of manufacture and therefore the price of the flux.

Certain undesirable impurities such as phosphorus, and sulphur etc are however kept to a minimum.

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Using natural minerals in flux formulations does add to the problems of the manufacturer, as different mines produce ores with different impurities, which can seriously, effect flux performance.

7.6 SMAW FLUX COATING

7.6.1 Addition of Elements Which Produce Slag

The molten puddle under the electrode has to be protected from the oxygen and nitrogen in the air.

The gases produced by vaporizing flux coating would not last long enough to protect the weld metal until it is fully solidified and cooled below a point where air would not hurt it. Therefore other elements are put into the flux coating to produce protective slag to keep the hot weld metal covered until it can expose to the air.

The molten slag is lighter in weight than the molten weld metal. It floats to the top of the weld puddle and hardens to protect the weld until it is cool. The slag also removes certain unwanted elements and impurities from the molten weld metal and base metal. When the weld is cool, the slag is removed and a bright, shiny weld will be found underneath.

7.6.2 Addition of Elements for the Stability of the Arc

Still other elements are put into the flux coating to help control the stability of arc under different conditions. Some flux additives are best for electrodes that operate with D.C. Other additives are best for electrodes that operate with A.C. still other additive make electrodes that can operate on either A.C., DCSP OR DCRP.

7.6.3 Addition of Deoxidizers

Some arc deoxidizers that help remove any excess oxygen in the weld metal created by rust or scale on the steel (the oxide residue floats out of the weld metal into slag). If these additives are present, the catalog description of the electrodes will tell you that it is “good for welding rusty or heavily scaled steel”.

7.6.4 Addition of Elements in the Flux for Fluidity

There are flux coating additives that help keep the molten weld metal from becoming too fluid. These are put into the flux to make the electrode work better for out of position welding.

7.6.5 Addition of Elements for High Deposition

Even more elements can be added to the flux to increase the deposition rate of finished weld metal. These additives are excellent for making high deposition rate SMAW electrodes that are only used in the flat position.

Iron powder in the coating improves arc behaviour, bead appearance, helps increase metal deposition rate and arc travel speed.

7.6.6 Addition of Elements for Reducing the Moisture Contents

Some electrodes even have additives in the flux coating that reduce the amount of moisture that the coating can pick up from humid air. These extra duty, moisture resistance electrodes are specially valuable for welding high strength low alloy steel and full alloy steel that are subject to

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hydrogen embrittlement. Even a tiny amount of moisture in your electrode flux can pass through the welding arc and become oxygen and hydrogen atoms and ions. The hydrogen will make high strength steel brittle.

7.6.7 Addition of Alloying Elements

Alloying elements like Ferro-alloys of manganese, molybdenum etc may be added to impart suitable properties and strength to the weld metal and to make good the loss of some of the elements, which vaporize while welding.

7.6.8 Binders

Binders are needed to hold the additives together, so that the flux would not chip off the electrode, and other chemical additives are needed to make it easy to extrude the flux coating on to the electrode wire.

7.7 MAIN CLASSES OF COVERINGS FOR SMAW ELECTRODES

7.7.1 Acid

The acid covering contain the largest amount of iron and manganese ores and alumina - silicates (high oxygen contents). This means that the covering is very active, because it contains both oxygen and hydrogen. The electrode can therefore be used for positional welding.

Welds made with acid electrodes usually have an excellent appearance, but poor mechanical properties. The welds-tends to be low in strength and for this reason acid electrodes are not widely used.

7.7.2 Rutile

The Rutile electrodes coverings, mainly contain TiO2 (Rutile). The transferred droplets are larger than the electrodes having acid coverings.

The arc is more stable but other differences from the acid electrodes type are small. Rutile electrodes are easy to operate and considered as good general purpose electrodes.

7.7.3 Cellulose

This type of electrode contain organic matter (usually cellulose) which often comprise about 30% by wt of total flux.

Zirconium silicate is often found in electrodes as both an arc stabilizer and an aid to slag detachability. With the oxygen and hydrogen contained in the covering, spray transfer occurs and the hydrogen aids good penetration which is of advantage in applications such as pipe welding.

7.7.4 Basic

The metal transfer observed when welding with basic covered electrode is by droplet, sometime large droplets and deoxidized low hydrogen metal is deposited.

Basic electrodes can be dried to sufficiently low moisture levels to give the low weld hydrogen contents which are required to minimise the risk of hydrogen cracking.

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Compared with the acid electrodes, partial pressure of hydrogen in the arc column gas is lower and hydrogen content of the weld joint will decrease because calcium fluoride combines with hydrogen at high temperature to produce hydrogen fluoride (HF). So basic electrodes are called low hydrogen type electrodes. They are capable of giving the low weld oxygen contents needed for the best weld toughness.

Table no. 7.2: Rough compositional ranges for the four main mma covering types weight %

Compound Acid Rutile Cellulose Basic TiO2 Trace-10 30 – 50 Trace - 5 Trace - 5 SiO2 10 - 20 5 – 15 5 - 15 5 - 15

ZrSiO4 Trace - 5 Trace – 5 Trace - 10 - CaCO3 5 - 15 15 – 25 5 - 15 25 - 40 CaF2 - - - 30 - 40 MnO 10 - 20 5 – 10 0 - 10 - MnO2 10-20 - - - FeO 10 - 20 5 – 10 0 - 10 - FeSi - - - 5 - 10 Mica - 10 – 20 - -

Ferro alloys - 0 – 5 - - Cellulose - - 25 - 40 -

7.8 AWS CLASSIFICATION

The welding material covered by the specification “A 5.1” “Specification for Carbon steel electrodes for Shielded Metal Arc Welding” are classified according to the following criteria.

1) Type of the current

2) Type of covering

3) Welding position of the electrode 4) Chemical composition of the weld metal

5) Mechanical properties of the weld metal in as welded condition

7.8.1 Prefix Letters

E = indicates an arc welding electrode, which, by definition, carries the arc welding current.

R = indicates a welding rod which is heated by means other then by carrying the arc welding current.

ER = indicates a filler metal, which may be used either as an arc welding electrode or as a welding rod.

EW = indicates a (non consumable) tungsten electrode

B = indicates a brazing filler metal

F = indicates a flux for use in submerged arc welding etc.

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AWS DESIGNATION TITLE OF SPECIFICATION A5.1 SPECIFICATION FOR CARBON STEEL ELECTRODES FOR SHIELDED METAL ARC WELDING

AWS EXXXX American Welding Society Electrode   First two digits of four digit numbers and Next to last digit indicates position e.g. first three digits of five digit numbers EXX1X All Positions indicates minimum tensile strength. EXX2X Flat & Horizontal Fillets e.g. EXX4X F, OH, H, V-Down E60XX 60000 psi Minimum Tensile strength E110XX 110,000 psi Minimum Tensile Strength Flux Coating (See table “7.3”) Electrode classification.

Table no. 7.3: Electrode classification.

AWS classification Type of covering

Capable of producing satisfactory welds in

position shown a Type of current b

E60 SERIES ELECTRODES E6010 High cellulose sodium F, V, OH, H DCEP E6011 High cellulose potassium F, V, OH, H AC or DCEP E6012 High titania sodium F, V, OH, H AC or DCEN E6013 High titania potassium F, V, OH, H AC or DC, either polarity E6020 High iron oxide H-fillets, F AC or DCEN E6022c High iron oxide F, H AC or DC, either polarity E6027 High iron oxide, iron powder H-fillets, F AC or DCEN

E70 SERIES ELECTRODES E7014 Iron powder, titania F, V, OH, H AC or DC, either polarity E7015 Low hydrogen sodium F, V, OH, H DCEP E7016 Low hydrogen potassium F, V, OH, H AC or DCEP E7018 Low hydrogen potassium, iron

powder F, V, OH, H AC or DCEP

E7024 Iron powder, titania H-fillets, F AC or DC, either polarity E7027 High iron oxide, iron powder H-fillets, F AC or DCEN E7028 Low hydrogen potassium, iron

powder H-fillets, F AC or DCEP

E7048 Low hydrogen potassium, iron powder

F, OH, H, V-down AC or DCEP

a. The abbreviations, F, V, V-down, OH, H, and H-fillets indicate the welding positions as follows : F =Flat, H = Horizontal, H-fillet =Horizontal fillets, V-down =Vertical down, V = Vertical

b. The term DCEP refers to direct current, electrode positive (DC reverse polarity). The term DCEN refers to direct current, electrode negative (DC straight polarity).

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7.8.2 AWS E6010

All position AWS E6010 electrodes are used for DCRP (electrode-positive) welding. They are best suited for making vertical and overhead welds.

The molten weld metal sprays through the welding arc something like a miniature paint gun. This spray transfer helps you weld in the vertical and overhead positions.

AWS E6010 electrodes give you deep weld penetration, which means that you have to be careful in handling the electrode to minimize spatter.

The thickness of the flux coating on AWS E6010 electrodes is held to a minimum to make it easier to weld in the vertical and overhead positions, but the coating will give you enough shielding for high-quality weld deposits. the electrode flux coating is high in cellulose, usually exceeding 30% cellulose by weight.

Some AWS E6010 electrode flux coatings have a small amount (less than 10 percent by weight) of iron powder in them to improve their arc characteristics. Because of the coating composition, these are generally classified as high cellulose sodium type electrodes.

7.8.3 AWS E6011

AWS E6011 electrodes are almost identical to AWS E6010 electrodes except that they operate on AC as well as DC. Their performance is very similar.

However, AWS E6011 electrodes perform equally well with either AC or DCRP (electrode- positive) power settings. These electrodes have a forceful digging arc action that results in deep base-metal penetration.

While the flux coating is slightly heavier than that of AWS E6010 electrodes, the resulting slag and weld profiles of AWS E6011 stick electrodes are quite similar to those of E6010 electrodes. The coating is high in cellulose and is designated as the high-cellulose potassium type. (potassium rather than sodium makes these electrodes work well with AC).

7.8.4 AWS E6012

The flux coating of AWS E6012 electrodes usually is high in titanium dioxide, exceeding 35 percent by weight, which is why these electrodes are often called titania or rutile coated grades.

AWS E6012 elelctrodes are characterized by medium penetration and dense slag which completely covers the bead.

AWS E6012 stick electrodes are used for all-purpose welding in all positions.

It is used much more frequently in flat and horizontal positions than in vertical or overhead welding.

They are especially recommended for single-pass, high-speed, high-current, horizontal fillet welds.

AWS E6012 electrodes have a rather quiet arc. This means that although you get medium base metal penetration, you also get a lot less spatter.

7.8.5 Low Hydrogen Electrodes

All low-hydrogen electrodes have a lot of calcium carbonate (the mineral in limestone) or calcium fluoride (a mineral called fluorite) in them. They sometimes are called lime-ferritic, or basic type electrodes. Materials such as cellulose, clays, asbestos, and other minerals that contain water in

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the crystal lattice are not used, to ensure that the electrode flux coating has a very low hydrogen content. (Because water is made of hydrogen and oxygen).

In addition, low-hydrogen electrodes are baked at higher temperatures after the flux has been extruded onto them to ensure that all the water possible has been driven out of the coating.

There must be no moisture, no organic materials and nothing else that might have hydrogen atoms in it, to prevent hydrogen embrittlement.

For the same reason you have to keep your electrode as dry as possible at all times.

When you use low hydrogen electrode, keep your arc to weld metal distance as short as possible to reduce the tendency for under bead cracking. Using a “short arc technique also will improve the quality of your as-welded deposit and will some what reduce the need for preheating and post- heating of difficult to weld steels.

7.8.6 Hydrogen Embrittlement

The hydrogen molecules when absorbed in steel produce very high stresses in the surface of the base metal. If the base metal is not very ductile, as in the case of most high strength steels, the metal acts like it has suddenly becomes very brittle. The result is a crack under the weld bead and is caused by hydrogen molecules being absorbed from the welding arc atmosphere into the weld metal and from there into the base metal.

“If you were told that you could only carry around two kinds of steel electrodes, your best choices would be AWS E6010 AND AWS E7018”.

7.8.7 AWS E7015

AWS E7015 electrodes are low hydrogen electrodes to be used with DCEP (electrode positive). The slag is chemically basic. The arc of E7015 electrodes is moderately penetrating. The slag is heavy, friable, and easy to remove. The shortest possible arc should be maintained for best results with E7015.

7.8.8 AWS E7016

AWS E7016 electrodes have all the characteristics of E7015 electrodes, plus the ability to operate on AC.

The core wire and coverings are very similar to those of E7015, except for the use of a potassium silicate binder or other potassium salts in the coverings to facilitate their use with AC.

7.8.9 AWS E7018

AWS E7018 electrode coverings are similar to E7015 coverings, except for the addition of a high percentage of iron powder. The coverings on these electrodes are slightly thicker than those of the E7015 and E7016electrodes. The iron powder in the coverings usually amounts to between 25 and 40 percent of the covering by weight.

7.9 ALLOY STEELS

Alloy steel may be defined as one whose characteristics properties are due to some elements other than carbon. Although all plain carbon steels contain moderate amount of manganese (up to about 0.90 % ) and silicon (up to about 0.30 %), they are not considered alloy steels because the principal function of the manganese and silicon is to act as deoxidizers. They combine with O2 and S to reduce the harmful effect of those elements.

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AWS DESIGNATIONTITLE OF SPECIFICATIONSA5.5SPECIFICATIONS OF LOW ALLOY STEEL ELECTRODES FOR SHIELDED METAL ARC WELDING Group of letters & numbers provides a clue to chemical composition of weld metal or may indicate a military or proprietary electrodes. Often a clue to impact strength or special heat treatment. AWS EXXXX-X American Welding Society Electrode   First two digits of four digit numbers and Next to last digit indicates position e.g. first three digits of five digit numbers EXX1X All Positions indicates minimum tensile strength. EXX2X Flat & e.g. Horizontal Fillets E70XX 70000 psi Minimum Tensile strength EXX4X F, OH, H, V-Down E110XX 110,000 psi Minimum Tensile Strength AWS A 5.5 includes more than 40 different classifications of low alloy steel electrodes for example:

AWS EXXXX - A1 ---------- CARBON MOLYBDENUM – STEEL ELECTRODES WITH Mo FROM 0.40 TO 0.65 % AWS EXXXX - B1 ------------- CHROMIUM - MOLYBDENUM STEEL ELECTRODES WITH Cr. AND Mo FROM 0.4 TO 0.65 %

------------------------- ------------------- etc.

The suffix (Example: EXXXX-A) indicates the approximate alloy in the weld deposit:

-A1 0.5 % Mo -B1 0.5 % Cr, 0.5% Mo -B2 1.25 % Cr, 0.5 % Mo -B3 2.25 % Cr, 1 % Mo -B4 2% Cr, 0.5 % Mo -B5 0.5% Cr, 1 % Mo -C1 2.5% Ni -C2 3.25% Ni -C3 1% Ni, 0.35 % Mo, 0.15% Cr -D1 and D2 0.25 - 0.45 % Mo, 1.75 % Mn -G 0.5% min. Ni, or 0.3% min. Cr, or 0.2% min. Mo, or 0.1% min. V, or 1% min. Mn (only one element required)

Flux Coating (See Table “4.3”) Electrode classification.

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AWS E 10018-M or AWS E 12018-M are a special military grade for welding sub marine hulls and test turrets.

7.10 ELECTRODES FOR GAS METAL ARC WELDING PROCESS (GMAW)

In Gas Metal Arc Welding (GMAW) an externally supplied shielded gas is used to protect the arc and molten weld metal from air. The filler metal is a continuous bare electrode wire fed through a wire feeder and a welding gun. The gun delivers both, the shielding gas and the electrode filler wire to the weld.

You can work continuously without stopping to change electrodes or pick up a new welding rod. The electrodes (filler metals) for gas metal arc welding are covered by various AWS filler metal specifications.

Generally for joining applications, the composition of the electrode (a filler metal) is similar to that of the base metal. The filler metal composition may be altered slightly to compensate for losses that occur in the welding arc, or to provide for deoxidation of the weld pool. In some cases, this involves very little modifications from the base metal composition.

AWS specification AWS A 5.18 “Carbon Steel Electrode and rods for Gas Shielded Arc Welding” on the basis of chemical composition of the wire and mechanical properties of the weld metal.

AWS DESIGNATION TITLE OF SPECIFICATION

A 5.18 SPECIFICATIONS FOR CARBON STEEL ELECTRODES AND RODS FOR GAS SHIELDED ARC WEDLING

SCOPE : This specifications prescribes requirements for bare carbon steel electrodes and rods for use with the GMAW, GTAW and PAW (Plasma Arc) welding processes.

CLASSIFICATION SYSTEM

(I) The classifications system used in this specifications follows as closely as possible the standard pattern used in other AWS filler metal specifications.

(II) As an example considerER70S-2

ER Bare filler metal may be used as an electrode or welding rod. 70 Indicates the required minimum Tensile Strength of the weld metal i.e. 70,000 Psi. S designates, a bare, solid electrode or Rod. 2 relates to the specific chemical composition for the filler metal. G For suffix G, (as in case of ER70S-G), no chemical requirements, with the exception that there will be no international addition of Ni, Cr, Mo or V. Subject to agreement between supplier and purchaser.

7.10.1 CHEMICAL COMPOSITION REQUIREMENTS

The chemical composition requirements for bare solid electrodes and welding rods are given in the following table.

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AWS Classification

C Mn Si P S Ni Cr Mo V Cu Ti Zr Al

ER 70S-2

0.07

0.90 to 1.40

0.40 to 0.70

0.025

0.035

c

c

c

c

0.50

0.05 to 0.15

0.02 to 0.12

0.05 to 0.15

ER 70S-3

0.06 to 0.15

0.90 to 1.40

0.45 to 0.70

-do-

-do-

-do-

-do-

-do-

-do-

-do-

----

----

----

ER 70S-4

0.07 to 0.15

1.00 to 1.50

0.65 to 0.85

-do-

-do-

-do-

-do-

-do-

-do-

-do-

----

----

----

ER 70S-5

0.07 to 0.19

0.90 to 1.40

0.30 to 0.60

-do-

-do-

-do-

-do-

-do-

-do-

-do-

----

----

0.50 to 0.90

ER 70S-6

0.07 to 0.15

1.40 to 1.85

0.80 to 1.15

-do-

-do-

-do-

-do-

-do-

-do-

-do-

----

----

----

ER 70S-7

0.07 to 0.15

1.50 to 2.00

0.50 to 0.80

-do-

-do-

-do-

-do-

-do-

-do-

-do-

----

----

----

ER 70S-G

No chemical requirements

7.11 STAINLESS STEEL ELECTRODES/RODS FOR GAS TUNGSTEN ARC

WELDING (GTAW) GTAW process is the most flexible of all fusion welding processes in terms of large variety of metals it can join.

Gas tungsten arc welding is not widely used in mass production for welding carbon and low alloy steel. The quality of gas tungsten arc welds in Carbon and alloy steels is more influenced by the base metal impurity content (i.e. sulphur, phosphorous, oxygen) than are welds made with SMAW or SAW. This is because fluxes are not present in GTAW to remove or tie up these impurities.

Stainless Steel :- Chromium is the major alloying element that makes stainless steels stainless or corrosion resistant.

Stainless steel and other alloys are extensively welded with the GTAW process because they are protected from the atmosphere by the inert gas.

Generally, the filler metal composition is adjusted to match the properties of the base metal in its welded condition.

AWS A 5.9 gives “specifications for base stainless steel welding electrodes and rods” as an example

AWS DESIGNATION TITLE OF SPECIFICATION

A 5.9 SPECIFICATIONS FOR BARE STAINLESS STEEL WELDING ELECTRODES AND RODS

The system of classification numbers used in this specification follows the standard pattern used in other filler metal specifications.

For example consider

AWS ER 308-L

Where AWS ----------- American Welding Society ER -------------- bare filler metal may be used as an electrode or welding rod. 308 ------------ indicates the chemical composition of filler metal. L --------------- indicates low carbon.

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7.12 WELDING OF ALUMINUM AND ALUMINUM ALLOYS

Aluminum and Aluminum alloys can be welded by GMAW or GTAW process.

But GTAW is ideally suited for welding of Aluminum alloys. Aluminum alloys form refractory surface Oxides which make joining more difficult. For this reason most welding of Aluminum is performed with alternating current, because it provide surface cleaning action.

Argon Shielding Gas is generally used for welding of Aluminum with alternating current because it provides better arc starting, better cleaning action.

7.13 ALUMINUM AND ALUMINUM ALLOY WELDING RODS AND BARE ELECTRODES AWS “A 5.10”

This specification prescribes Aluminum and Aluminum alloys welding rods for use with TIG welding.

Rods and electrodes are classified on the basis of chemical composition of the as manufactured filler metal.

The letter system for identifying the filler metal classifications in this specification follows the standard pattern used in other AWS filler metal specifications.

ER Bare filler metal may be used as an electrode or welding rod

The Aluminum association alloy designation nomenclature is used for the numerical portion to identify the alloy.

e.g.

Aluminum of 99 % minimum purity 1XXX Copper 2XXX Manganese 3XXX Silicon 4XXX Magnesium 5XXX Magnesium & Silicon 6XXX Zinc 7XXX Other element 8XXX Unused series 9XXX

7.14 SHIELDING GASES

7.14.1 General

The primary function of the shielding gas is to exclude the atmosphere from contact with the molten weld metal. This is necessary because most metals, when heated to their melting point in air, exhibit a strong tendency to form oxides and, to a lesser extent nitrides. Oxygen will also react with Carbon in molten steel to form Carbon monoxide and Carbon dioxide. These varied reaction products may result in weld deficiencies, such as trapped slag, porosity and weld metal embrittlement. Reaction products are easily formed in the atmosphere unless precautions are taken to exclude Nitrogen and Oxygen.

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In addition to provide a protective environment, the shielding gas and their flow rate also have a pronounced effect on the following.

1. Arc characteristics. 2. Mode of metal transfer. 3. Penetration and weld bead profile. 4. Speed of welding. 5. Under cutting tendency. 6. Cleaning action. 7. Weld metal mechanical properties.

7.14.2 Argon

Commercial grade purity 99.996 % is obtained by fractional distillation of liquid air from the atmosphere, in which it is present to about 1 % (0.932 %) by volume. It is supplied in blue- painted cylinders. Argon is the most common shielding gas used for both GMAW and GTAW to joint Aluminum and Stainless steel.

The reasons for its popularity, its cost is less than Helium and it makes welding easy. Argon has low ionization potential. Argon freely, given up electrons, which produce a more stable and quite arc during welding, such arc stability means less spatter.

The lower ionization potential reduces the arc voltage, creating the lower power in the arc, and therefore lower joint penetration, and poor bead contour.

When welding heavier steel plates Argon is generally mixed with other gases to produce a more effective shield, which improves bead contour, appearance and penetration.

High density of Argon reduce flow rates. More shielding gas flow is needed for lighter Helium than heavier Argon gas when working down hand.

For working over head, less Helium than Argon gas may be needed because Helium is so light it rises up against over head weld metal.

Argon also produces spray transfer and that is a big factor in its use in GMAW. Not a high energy input gas, Argon makes a weld that freezes quickly. If the metal is not molten long enough to wet out to the weld toe, under cutting results. For Ferrous materials, additions of 1 to 5 % Oxygen, which super heat the metal allows the molten weld metal shielded by Argon to flow out to the toes of the weld and help avoid undercutting.

7.14.3 Helium

Helium, the next most abundant inert gas, available for shielding welds. Arc stability depends on shielding gas’s ionization potential. The low ionization potential of Argon turns atoms into ions easily which helps to sustain a smooth, even arc.

Whereas, Helium has a higher ionization potential than Argon. Therefore Helium shielded welding produces a less stable arc.

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Arc and puddle control are difficult when using pure Helium shielding gas compared with Argon or an Argon-Helium Argon- CO2 or Argon-O2 gas mixture. Helium can also present problems in arc initiation.

Arcs shielded only by Helium do not exhibit true axial spray transfer at any current level. The result is that Helium-shielded arcs produce a more spatter and have rougher bead surfaces than Argon-shielded arc.

Helium costs more per unit volume than does Argon or CO2, but it allows fast welding with narrow gaps.

7.14.4 Carbon Dioxide

Carbon Dioxide (CO2) is a reactive gas, widely used in its pure form for GMAW of carbon and low alloy steel. It is the only reactive gas suitable for use alone as a shield in the GMAW process. Higher welding speed, greater joint penetration, and lower cost are general characteristics which have encouraged extensive use of CO2 shielding gas.

Major disadvantage of the use of CO2 is its extreme resistance to current flow. Because of this resistance, the arc length is sensitive. When the arc length is too long, it will extinguish more readily than when an inert gas, like Argon or Helium is used.

7.15 CARE AND STORAGE OF ELECTRODES

Utmost care is required in handling and storage of electrodes. Electrodes coating should neither get damped nor be damaged or broken.

Electrodes with damped coating will produce a violent arc, porosity and cracks in the joint. Electrodes with damaged coating will produce joints of poor mechanical properties.

To avoid damage to coating (a) electrodes during storage should neither bend nor deflect, (b) Electrode packets should not be thrown are piled over each other.

Electrodes should be stored in a dry and well ventilated store rooms. Storage temperature of air should be about 20 °C and relative humidity 50% maximum. Cellulose electrodes are not so critical but they should be protected against condensation.

Before use the electrodes may be dried as per manufacturer's recommendations.

Electrodes should preferably be retained in original (manufacturer's) packing for identification. Loss of identity of electrodes can waste a lot of time in recognizing them correctly.

7.16 TUNGSTEN ELECTRODES

AWS CLASSIFICATION OF TUNGSTEN ARC WELDING ELECTRODES (AWS A5.12)

7.16.1 Introduction

Tungsten electrodes are non consumable in that, they do not intentionally become part of a welded joint as do other electrodes used as filler metals.

The function of a tungsten electrode is to serve as one of the terminals of an arc, which supplies the heat required for welding.

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7.16.2 Classification

The Tungsten Electrodes are classified on the basis of their chemical composition.

They are classified into different groups i.e.

1. EWP 2. EWTh 3. EWCe 4. EWLa 5. EWZr

A classification designation used for Tungsten Electrodes are similar to those used for AWS filler metals in general i.e.

AWS EWP

AWS = American Welding Society

E = Stands for Electrode

W = Stands for Tungsten

P = Stands for pure Tungsten

Th = Thoriated Tungsten

Zr = Zirconiated Tungsten etc.

7.16.3 Operation and Usability

The choice of an Electrode Classification, size and welding current is influenced by the type & thickness of the base metals to be welded. The capacity of Tungsten Electrode to carry current is dependent upon numerous other factors, including i.e.

 Type & polarity of the current

 Shielding gas used

 Type of equipment used (air or water cooled)

 The extension of the electrode beyond the collet & welding position

1. An electrode of given size will have its greatest current capacity with direct current (straight polarity) (DCSP), less with alternating current and still less with direct current reverse polarity (DCRP).

2. Tungsten has a very low electrical conductivity and therefore, heats up when current is passed through it. When welding with tungsten electrodes, the arc tips should be only hot part of the electrode, the remainder should be kept as cool as possible.

3. One method of preventing electrode overheating is to keep the extension of the electrode from the collet short. If the extension is too large, even or relatively low current can cause the electrode to overheat.

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7.16.4 Colour Code and Alloying Elements for Various Tungsten Electrode Alloys

AWS classification Colour

a Alloying element Alloying oxide Nominal weight of

alloying oxide percent

EWP Green - - - EWCe-2 Orange Cerium CeO2 2 EWLa-1 Black Lanthanum La2O3 1 EWTh-1 Yellow Thorium ThO2 1 EWTh-2 Red Thorium ThO2 2 EWZr-1 Brown Zirconium ZrO2 .25

a) Colour may be applied in the form of bands, dots, etc., at any point on the surface of the electrode.

7.16.5 EWP Electrode Classification (Pure Tungsten)

Pure tungsten electrodes (EWP) contain a minimum of 99.5 percent tungsten, with no intentional alloying elements. The current carrying capacity of pure tungsten electrodes is lower than that of the alloyed electrodes. Pure tungsten electrodes are used mainly with ac for welding aluminum and magnesium alloys. The tip of the EWP electrode maintains a clean, balled end, which provides good arc stability. They may also be used with dc, but they do not provide the arc initiation and arc stability characteristics of thoriated, ceriated, or lanthanated electrodes.

7.16.6 Tungsten - Thorium Alloys (Ewth Electrode Classification)

The thermionic emission of tungsten can be improved by alloying it with metal oxides that have very low work functions. As a result, the electrodes are able to handle higher welding currents without failing. Thorium oxide (ThO2) is one such addition. Two types of thoriated tungsten electrodes are available. The EWTh-1 and EWTh-2 electrodes contain 1 % and 2% thorium oxide (ThO2) called thoria respectively, which is evenly dispersed through their entire lengths. A discontinued classification of tungsten electrodes is EWTh-3 class.

i. Thoriated tungsten electrodes are superior to pure tungsten electrodes in several respects i.e.

ii. The thoria provides about 20 % higher current carrying capacity. iii. Generally longer life. iv. Greater resistance to contamination of the weld. v. Arc starting is easier and the arc is more stable than pure tungsten or zirconiated

tungsten electrodes.

vi. The EWTh-1 & EWTh-2 electrodes were designed for DCSP applications. They maintain a sharpened tip configuration during welding, which is desirable for welding steel.

vii. They are not often used with AC because it is difficult to maintain the balled end, which is necessary with AC welding, without splitting electrode.

viii. Thorium is a very low-level radioactive material. The level of radiation has not been found to represent a health hazard. However, if welding is to be performed in confined spaces for prolonged periods of time, or if electrode-grinding dust might be ingested, special precautions relative to ventilation should be considered. The user should consult the appropriate safety personnel.

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7.16.7 EWCe Electrodes Classification

Ceriated tungsten electrodes were first introduced into the united state market in the early 1980’s.

These electrodes were developed as possible replacements for thoriated electrodes because cerium, unlike thorium, is not a radioactive element. The EWCe-2 electrodes are tungsten electrodes containing 2 % cerium oxide (CeO2) referred to as ceria. EWCe-2 electrodes will operate successfully with AC or DC.

7.16.8 EWLa Electrode Classification

The EWLa-1 electrodes were developed around the same time as the ceriated electrodes and for the same reason, that lanthanum is not radioactive. These electrodes contain 1 percent lanthanum oxide (La2O3), referred to as lanthana. The advantages and operating characteristics of these electrodes are very similar to the ceriated tungsten electrodes.

7.16.9 EWZr Electrode Classification

Zirconiated tungsten electrodes (EWZr) contain a small amount of zirconium oxide (ZrO2), as listed in Table. Zirconiated tungsten electrodes have welding characteristics that generally fall between those of pure and thoriated tungsten. They are the electrode of choice for ac welding because they combine the desirable arc stability characteristics and balled end typical of pure tungsten with the current capacity and starting characteristics of thoriated tungsten. They have higher resistance to contamination than pure tungsten, and are preferred for radiographic-quality welding applications where tungsten contamination of the weld must be minimized.

7.16.10 Electrode Tip Configurations

The shape of the tungsten electrode tip is an important process variable in GTAW. Tungsten electrodes may be used with a variety of tip preparations. With ac welding, pure or zirconiated tungsten electrodes form a hemispherical balled end. For dc welding, thoriated, ceriated, or lanthanated tungsten electrodes are usually used. For the latter, the end is typically ground to a specific included angle, often with a truncated end.

In general as the included angle increases, the weld penetration increases and the width of the weld bead decreases.

Regardless of the electrode tip geometry selected, it is important that consistent electrode geometry be used once a welding procedure is established.

7.16.11 Electrode Contamination

Contamination of the tungsten electrode is most likely to occur when a welder accidentally dips the tungsten into the molten weld pool or touches the tungsten with the filler metal. The tungsten electrode may also become oxidized by an improper shielding gas or insufficient gas flow, during welding or after the arc has been extinguished.

The contaminated end of the tungsten electrode will adversely affect the arc characteristics and may cause tungsten inclusions in the weld metal. If this occurs, the welding operation should be stopped and the contaminated portion of the electrode removed.

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